Field of the Invention
The present invention relates to a multilayer structure and a laminate structure obtained by using the multilayer structure. Specifically, the present invention relates to a multilayer structure capable of suppressing reflected light at a wavelength λ intended to prevent reflection and a laminate structure obtained by using the multilayer structure.
Background Art
In recent years, as one of energy saving measures for reducing carbon dioxide, heat ray shieldability-imparting materials have been developed for windows of vehicles and buildings. From the viewpoint of heat ray shieldability (solar heat gain coefficient), desired are heat reflective types with no reradiation rather than heat absorbing types with indoor reradiation of absorbed light (in an amount of about ⅓ of the absorbed solar energy), for which various proposals have been made.
For example, a thin metal film of Ag is generally used as a heat ray reflecting material since the reflectance is high, but reflects not only visible light or heat rays but also radio waves, and thus has a problem in that the visible light transmittance and the radio wave transmittance are low. For increasing the visible light transmittance, Low-E glass (for example, manufactured by Asahi Glass) using a multilayer film of Ag and ZnO is widely used in buildings, but the Low-E glass has a problem in that the radio wave transmittance is low since a metal thin film of Ag is formed on the glass surface.
As a method for solving the problem, Patent Reference 1 discloses a heat ray shielding material which has a metal particles-containing layer containing at least one type of metal particle, in which the metal particles are tabular metal particles having a substantially hexagonal to circular forms in a ratio of at least 60% by number and the main plane of tabular metal particles is plane-oriented in a range of 00 to ±300 relative to one surface of the metal particles-containing layer. With this configuration, it is possible to provide a heat ray shielding material which has high reflection wavelength selectivity and reflection bandwidth selectivity, and excellent transmittance at a wavelength intended to prevent reflection.
Further, in regard to a radio wave transmissible wavelength selection plate formed by providing a layer made of Ag fine particles on a transparent substrate, Patent Reference 2 discloses that inconvenience in which diffused reflection in a wavelength range of visible light becomes increased can be solved when a resonant wavelength is adjusted to be in the range of 600 nm to 1500 nm for the purpose of increasing a near-infrared ray shielding factor (Es) using the radio wave transmissible wavelength selection plate in which a transparent dielectric layer having a dielectric constant greater than that of the transparent substrate forms a film having an optical film thickness of 20 nm to 600 nm and a layer formed of Ag fine particles is formed on the dielectric layer.
However, the method described in Patent Reference 1 is only to provide a dielectric layer for changing the resonant wavelength of the Ag film and a concept of suppressing intensity of reflected light of the Ag film has not been researched. Further, in the Patent Reference 1, the relationship between the wavelength intended to suppress the reflected light and the film thickness of the dielectric layer has not been researched.
Patent Reference 3 discloses a front plate which is placed on the front surface of a display panel and used for preventing reflection, shielding electromagnetic waves, and the like. Further, Patent Reference 3 described that a screen which is excellent in terms of preventing reflection, cutting electromagnetic waves, and cutting infrared rays and has excellent transparency can be displayed by means of using a front plate for display in which a first anti-reflection film is provided on a surface on an observer side of a transparent base substrate through an adhesive layer, and a filter film for cutting near-infrared rays and shielding electromagnetic waves and a second anti-reflection film are respectively disposed in order through the adhesive layer on the surface on the opposite side of the surface on the observer side of the base substrate.
However, a mesh formed of a metallic thin film or an ITO film is exemplified as a filter film for cutting near-infrared rays or shielding electromagnetic waves in Patent Reference 2. They are heat absorbing types, a configuration of a heat reflective type is not described in Patent Reference 2, and research on a transmission spectrum is only made in Examples and a reflection spectrum is not researched. In addition, in Patent Reference 2, even though an anti-reflection film having an anti-reflection layer (AR) is arranged on both surfaces of the filter film for cutting near-infrared rays or shielding electromagnetic waves, the anti-reflection film is not arranged such that optical interference between the anti-reflection film and the filter film for cutting near-infrared rays or shielding electromagnetic waves may occur, and accordingly, the reflected light from the filter film for cutting near-infrared rays or shielding electromagnetic waves cannot be suppressed. Moreover, as the anti-reflection layer (AR) in Patent Reference 2, a layer obtained by alternately laminating a high refractive index layer such as a Ti oxide or zirconium and a low refractive index layer of a silicon oxide can be exemplified, but this layer is also a heat absorbing type and does not have a configuration of a heat reflective type.